Also, larger shops, like the ones found in the main cities would have a higher
balance, thus accepting more items before the value starts decreasing, than
smaller shops, like the ones found in player cities. Still, with a fluctuating
buy rate for the shops, people would be encouraged to seek out different
shops, thus moving around more. Would make it worth your wile to seek out
smaller shops in less visited places.

Maybe the shops also could have a more stable variable (that isn't reset at
boot) that allow them to grow bigger and be able to buy in more stuff at
higher rates in the long run.

CM